Skewed antenna array



May 26, 1959 R. w. MASTERS SKEWED ANTENNA ARRAY Filed Dec. 31. 1953Robe-r2 Wjl Z Zefs ATTORNEY United States Patent 2,888,677 Patented May26, 1959 SKEWED ANTENNA ARRAY Robert W. Masters, Columbus, Ohio,assignor to Radio Corporation of America, a corporation of DelawareApplication December 31, 1953, Serial No. 401,58ti

8 Claims. (Cl. 343-798) This invention relates to skewed antenna arrays,and more particularly, to antenna arrays wherein a plurality of antennaelements are mounted around the surfaces of a tower or buildingstructure which is relatively large in cross-section, each antennaelement being arranged to have maximum gain in a direction parallel withthe corresponding surface. A symmetrical array provides substantiallyuniform field strength in all directions in a horizontal plane aroundthe tower.

It is known to provide broadcast antenna arrays by mounting a pluralityof half-wave dipole antenna elements around the four side surfaces of atower having width dimensions in the order of a half wavelength, thedipoles being disposed parallel with the corresponding side surfaces.Since the cross-sectional or width dimensions of the tower are of thesame order as the length of the dipoles, the resulting gain or fieldstrength in all directions in the horizontal plane is substantiallyuniform. At higher frequencies, the cross-sectional dimension of thetower must be correspondingly reduced in order to obtain uniform gain inall horizontal directions. The limitation on the cross-sectionaldimension of the tower may be such that the tower would haveinsuflicient structural strength.

Occasions arise where it is desired to radiate relatively high frequencyenergy from an existing tower or building structure having such across-sectional dimension as to preclude obtaining an omni-directionalresponse in the horizontal plane by following conventional antennadesign practices. It is therefore a general object of this invention toprovide an antenna array providing an omnidirectional pattern from atower or building structure having a cross-sectional dimension which islarge relative to the wave-length of the energy handled.

In most communities there are relatively few advantageous sites forradio and television broadcasting antennas. The best site is often thetop of the tallest building in the community. In this event, it may bedesirable to mount all radio and television antennas serving thecommunity at the top of a single building. It is especially desirablethat all television antennas serving a community be located at or nearthe same point so that all of the directional receiving antennas may bedirected in one direction to receive all broadcasts.

It is therefore desirable to interlace two or more antenna arrays on thesame vertical portion of a single tower. However, a tower designed forradiating channel 2 television signals in the range of from 54 to 60megacycles will have too great a cross-sectional dimension to supportantenna elements for channel 9, operating in the range of from 186 to192 megacycles, if the antenna array is constructed according toconventional techniques. It is therefore another object of thisinvention to provide interlaced antenna arrays operating at widelydifferent frequencies and all mounted on a single tower to provideomni-directional patterns in the horizontal plane.

It is a further object of this invention to provide imlel with thecorresponding tower side.

proved omni-directional antenna arrays characterized by simplicity ofconstruction, ease of tuning, and low wind resistance.

In one aspect, the invention comprises a vertical tower of squarecross-section having four conductive side surfaces such as may beprovided by conductive screens attached to the structural members of thetower. Vertical reflectors are mounted perpendicular to the four sidesof the tower near the centers thereof. A quarter-wave unipole ispositioned near each reflector, the dipoles being on the same sides ofthe reflectors whenviewed by going around the tower in one direction.The unipoles extend perpendicular with the tower sides and eachreflector and unipole combination has greatest gain in a directionparal- The directions of greatest gain are the same when viewed goingaround the tower in one direction. The combined effects of the fourreflector and unipole combinations is a substantially uniform pattern inall directions around the tower in the horizontal plane.

In another aspect, the invention comprises an antenna tower provided onthe four faces or sides thereof with half-wave antenna elements ordipoles for operation at a first frequency. The tower sides are about ahalf-wavelength at the first frequency so that each dipole has greatestgain in a direction perpendicular with the corresponding tower side. Oneor more additional sets of four quarter-wave unipoles are mounted on thetower sides, together with vertically disposed reflectors, to pro videoperation at one or more higher frequencies. Each quarter-wave unipoletogether with the associated reflector provides a pattern havinggreatest gain in a direction parallel with a corresponding tower side.By this construction, a single tower supports two or three antennaarrays operating at three different frequencies, all being substantiallyomni-directional in the horizontal plane. A plurality of bays orsections of the three antenna arrays may be arranged along the verticallength of the tower to provide maximum gain in the vertical planes atthe surface of the earth.

These and other objects and aspects of the invention will be moreapparent to those skilled in the art from the following descriptiontaken in conjunction with the appended drawings, wherein:

Fig. l is a sectional view taken in a horizontal plane showing avertical tower provided with an antenna array which provides asubstantially omni-directional pattern in the horizontal plane;

Fig. 2 is an elevation of the antennaarray shown in Fig. 1;

Fig. 3 is a sectional view taken in a horizontal plane showing avertical tower provided with three antenna arrays operative at threedifferent frequencies, and all providing omni-directional patterns inthe horizontal plane;

Fig. 4 is an elevation of the antenna array shown in Fig. 3;

Fig. 5 is a fragmentary perspective view of a quarterwave unipole suchas may be employed in the antenna arrays of Figs. 1 thru 4; and

Fig. 6 is a fragmentary perspective view of a half-wave dipole such asmay be used in the antenna array of Figs. 3 and 4.

Referring to the omni-directional antenna array shown in Figs. 1 and 2,a tower or building structure having a square cross-section is shown bythe outline formed by the four sides 8, 9, 10 and 11. The sides of thetower are conductive surfaces which may be inherent in the towerconstruction itself or may be provided by electrically conductivescreens secured to the sides of the tower. The width dimension of eachof the tower sides 8, 9, 10

and 11 is large compared with the wavelength at which the desiredantenna array is to operate. In other words, the widths of the sides arelarge compared with a halfwavelength at the operating frequency.

Vertically arranged metallic wave reflecting screens 12, 13, 14 and 15are connected along one edge to the sides 8, 9, 10 and 11, respectively.The reflector screens extend at right angles from the tower sides.

Quarter-wave unipoles 18, 19, 2t) and 21 are mounted to extendperpendicular with the respective tower sides 8, 9, 10 and 11 at pointsspaced from the corresponding reflector screens. The quarter-Waveunipoles are all on the same sides of the associated reflector screenswhen viewed by going around the tower in one direction. Referring toFig. l, the quarter-wave unipole 18 and reflector screen 12 result in apattern having greatest gain parallel with the side 8 and extending tothe right as shown by the dotted line pattern. Similarly, the otherunipole and reflector screen combinations have a pattern with greatestgain in the direction parallel with the corresponding tower side, thedirections being the same when considered by an observer going aroundthe tower in a clockwise direction.

The quarter-wave unipoles may be fed in phase, or in quadrature phasesequence, depending upon the midth dimensions of the tower. The feedarrangement is designed by taking into account the width of the sides ofthe tower so as to provide patterns from the four antennas which add upvectorially to provide an omni-directional pattern in the horizontalplane.

Figs. 3 and 4 show three antenna arrays operative at three differentfrequencies and all mounted on the same vertical tower. The tower andone of the antenna arrays is the same as that shown in Figs. 1 and 2,and the same reference numerals have been used to designate thecorresponding elements. The only difference is that a plurality ofvertically spaced quarter-wave unipoles and halfwave dipoles are mountedon each tower side.

In addition, the antenna of Figs. 3 and 4 includes a plurality ofquarter-wave unipoles 28 on tower side 8, a plurality of quarter-waveunipoles 29 on tower side 9, a plurality of quarter-wave unipoles 30 ontower side 10 and a plurality of quarter-wave unipoles 31 on tower side11. The unipoles 28, 29, 30 and 31 are longer than the unipoles 18, 19,2t) and 21, and are positioned on the corresponding tower sides onopposite sides of the reflectors 12, 13, 14 and 15. Both the unipoleantenna array and dipole antenna array utilize the common reflectors 12,13, 14 and 15. The pattern of unipole 28 has a maximum gain in adirection to the left and parallel with the tower side 8. The patternsof unipoles 29, 30 and 31 similarly have maximum gain in directionsparallel with the corresponding tower sides, all the directions beingcounter-clockwise, and opposite to the clockwise direction of radiationfrom unipoles 18 to 21. Like the antenna array including unipoles 18thru 21, the second antenna array including unipoles 28 thru 31 has anomni-directional pattern in the horizontal plane. All of thequarter-Wave unipoles may be fed in any convenient manner such as by acoaxial line as shown in Fig. wherein the outer conductor of the coaxialline is connected to the tower side, and the inner conductor is extendedto form the radiating element.

A third antenna array for operation at a third frequency lower than thefrequencies of the first and second arrays, comprises half-wave dipoles38, 39, 4t) and 41 mounted parallel with the corresponding tower sides8, 9, and 11. The half-wave dipoles may be connected to coaxialtransmission lines in the manner illustrated in Fig. 6, or in any othersuitable manner.

It will be noted that the half-wave dipoles 38, 39, 4t and 41 havelengths which correspond roughly with the widths of the tower sides, andthat the half-wave dipoles are arranged parallel with the correspondingtower sides. By this construction, each half-wave dipole has a patternwith maximum gain in the direction perpendicular with the correspondingtower side. The vector addition of the patterns of the four half-wavedipoles is such that the half-wave dipole array provides anomni-directional pattern in the horizontal plane.

The antenna shown in Figs. 3 and 4 may, for example, be employed intelevision broadcasting for the simultaneous transmission of threetelevision signals of different frequencies. The first antenna arrayincluding quarter-wave unipoles 18 thru 21 may be, employed to broadcastthe signal of highest frequency, for example, a channel 13 signal havinga frequency in the range of from 210 to 216 megacycles. The secondantenna array including quarter-wave unipoles 28 thru 31 may be employedto broadcast an intermediate frequency signal, such as a channel 9signal having a frequency range of from 186 to 192 megacycles. The thirdantenna array including half-wave dipoles 38 thru 41 may be employed tobroadcast a television signal of lower frequency, such as for example, achannel 2 signal having a frequency in the range of from 54 tomegacycles.

The three antenna arrays occupy the same vertical portion of the towerand yet they do not interfere one with the other. There is very littlecoupling between the first antenna array including quarter-wave unipoles18 thru 21, and the second antenna array including quarter-wave unipoles28 thru 31 because the tower sides are wide in terms of wavelengths, andbecause of the isolation effected by the reflector screens 12 thru 15.There is practically no coupling between the third antenna arrayincluding half-wave dipoles 38 thru 41 and the first and second antennaarrays because of the widely spaced operating frequencies thereof andbecause the antenna arrays are operatively oriented at right angles witheach other. The isolation betweenthe third antenna array and the firsttwo is further improved when, as is preferred, the antenans of the firstand second arrays are fed in phase, and the antennas of the third arrayare fed in quadrature sequence.

It will, of course, be understood that Fig. 4 shows one vertical sectionor bay of a complete antenna which may include a plurality of similarsections or bays mounted one above the other to provide the desireddirectivity in vertical planes.

It is apparent that, according to the construction shown in Figs. 3 and4, two additional higher frequency antenna arrays may be added to anexisting tower on which there is a half-wave dipole antenna array ofconventional design. The two additional higher frequency antenna arraysoccupy the same vertical section of the tower as the existing lowerfrequency antenna array without interference between the arrays.

If a pattern in the horizontal plane other than omnidirectional isdesired, antennas may be mounted only on any two or three tower sides toprovide any desired pattern in the horizontal plane. To obtain someirregular patterns, it may be necessary to unequally distribute radiofrequency power to the several antennas.

What is claimed is:

1. An antenna comprising a vertical tower of rectangular cross-sectionhaving four conductive sides, four reflector screens, one of saidscreens being secured on one edge thereof intermediate the edges of eachof said sides of said tower in a vertical position and extending atright angles therewith, a first antenna array comprising fourquarter-wave unipoles each mounted perpendicularly on one of said towersides in spaced relation with the corresponding one of said screens, allof said unipoles being on the same side of said screens when viewedgoing around said tower in one direction, and a second antenna arraycomprising four quarter-wave unipoles each mounted perpendicularly onone of said tower sides in spaced relation with the corresponding one ofsaid reflector screens, all of said unipoles of said secondary human 1array being on the opposite sides of said reflector screens with respectto said unipoles of said first array.

2. An antenna comprising a vertical tower of rectangular cross-sectionhaving four conductive sides, four reflector screens, one of saidscreens being secured at one edge to each of said sides of said tower ina vertical position and extending at right angles therewith, at leastfour quarter-wave unipoles, one of said unipoles being mountedperpendicularly on each of said tower sides in spaced relation with thecorresponding one of said reflector screens, all of said unipoles beingon the same side of said reflector screens when viewed going around saidtower in one direction, and four half-wave dipoles, one of said dipolesbeing mounted on each of said tower sides.

3. Antenna arrays as defined in claim 2, wherein said tower sides eachhave a width in the order of a halfwavelength at the operating frequencyof said half-wave dipoles, and wherein said quarter-wave unipoles areoperative at a higher frequency.

4. Three antenna arrays mounted on a tower comprising a vertical towerhaving four conductive sides arranged generally in the form of a square,four reflector screens, one of said screens being secured on one edge toeach of said sides of said tower in a vertical position intermediate theedges of said side and extending at right angles therewith, a firstantenna array including in combination with said reflector screens aplurality of quarterwave unipoles each mounted perpendicularly on one ofsaid tower sides in spaced relationship with said reflector screens onthe same sides thereof when viewed going around said tower in onedirection, a second antenna array including in combination with saidreflector screens a plurality of quarter-wave unipoles each mountedperpendicularly on one of said tower sides in spaced relationship withsaid reflector screens on opposite sides thereof from the unipoles ofsaid first antenna array, and a third antenna array including fourhalf-wave dipoles each mounted on one of said four tower sides.

5. Antenna arrays as defined in claim 4, wherein said tower sides have awidth in the order of a halfwavelength at the operating frequency ofsaid half-wave dipoles constituting said third array, and wherein saidquarter-wave unipoles constituting said first and second arrays areoperative at diflerent frequencies higher than the operating frequencyof said third antenna array.

6. Antenna arrays as defined in claim 5, wherein said half-wave dipolesconstituting said third antenna array are mounted in spaced parallelrelation with said corresponding sides by means of parallel spacedsupports extending from said tower sides, and wherein said reflectorscreens are mounted on said tower sides between said supports.

7. Antenna arrays as defined in claim 4, wherein the unipolesconstituting said first array are fed in phase, said unipolesconstituting said second array are fed in phase, and said dipolesconstituting said third array are fed in quadrature sequence.

8. An antenna array comprising a structure having at least threeconductive sides connected together to form a structure having apolygonal transverse cross-section and having an axis, an individualradiator screen fastened to each of said sides, said screens extendingfrom their respective sides at substantially a right angle with respectthereto and in planes parallel to said axis of said structure, anindividual quarter-wave unipole mounted on each of said sides oncorresponding sides of said screens when viewed going around saidstructure in one direction, and an individual half-wave dipole mountedon each of said sides.

References Cited in the tile of this patent UNITED STATES PATENTS2,444,320 Woodward June 29, 1948 2,471,515 Brown May 31, 1949 2,539,433Kandoian Jan. 30, 1951 2,637,815 Shanklin May 5, 1953 2,653,238Bainbridge Sept. 22, 1953 2,808,585 Andrew Oct. 1, 1957

